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Fusarium crown rot (FCR), caused predominantly by Fusarium pseudograminearum (Fp) in Australia, is an important fungal disease of wheat and barley. FCR causes significant yield losses and reduced grain quality worldwide. This study investigated the population dynamics of FCR‐causing F. pseudograminearum isolates from Western Australia (WA), a major wheat‐growing region. Wheat samples were collected from a total of seven different sites in 2008 and 2015. Two sites, Tammin and Karlgarin, with moderate to high FCR incidence, were intensively sampled in both years. The results revealed significant increase in Fp isolation frequency between 2008 and 2015. Over 86% of 1100 Fusarium isolates were Fp in 2015 compared with 59% of 639 isolates from 2008. Mating type idiomorphs, toxin chemotypes and population genetic structures were determined for a subset of 279 Fp isolates (132 isolates from 2008 and 165 from 2015). Mating type analysis revealed differences in MAT1‐1 and MAT1‐2 distributions between Tammin and Karlgarin for both years. Results also showed that 97.6% of Fp isolates analysed had the 3‐ADON trichothecene chemotype. Additionally, for the first time in Australia, the 15‐ADON chemotype was identified in 2.3% and 2.4% of Fp isolates from 2008 and 2015, respectively. The genetic structure of Fp population determined using 21 cleaved amplified polymorphic sequence (CAPS) markers revealed a high level of genetic variation within and between populations. In addition, 2015 isolates from Tammin and Karlgarin were significantly more aggressive (P < 0.0001) than 2008 isolates. This finding may have implications in managing this significant fungal disease. [ABSTRACT FROM AUTHOR]

This study examines the CO2-mediated influence of plant resistance on crown rot dynamics under continuous cropping of partially resistant wheat line 249 and the susceptible cultivar Tamaroi. Disease incidence, severity, deoxynivalenol and Fusarium biomass were assessed after each cycle in microcosms established at ambient and 700 mg kg-1 CO2 using soil and stubble of these wheat lines from a field experiment with free to air CO2 enrichment. Monoconidial isolates from wheat stubble were collected initially, and after five cropping cycles, to compare the frequency and aggressiveness of Fusarium species in the two populations. Aggressiveness was measured using a high-throughput seedling bioassay. At elevated CO2, the higher initial incidence in Tamaroi increased with cropping cycles, but incidence in 249 remained unchanged. Incidence at ambient CO2 did not change for either line. Elevated CO2 induced partial resistance in Tamaroi, but not in 249. Increased Fusarium biomass in wheat tissue at elevated CO2 matched raised deoxynivalenol of the stem base in both lines. After five cycles of continuous wheat cropping, aggressiveness increased in pathogenic F. culmorum and F. pseudograminearum by 110%, but decreased in weakly pathogenic F. equiseti and F. oxysporum by 50%. CO2 and host resistance interactively influenced species frequency, and the highly aggressive F. pseudograminearum became dominant on Tamaroi irrespective of CO2 concentration, while its frequency declined on 249. This study shows that induced resistance at elevated CO2 will not reduce crown rot severity, or impede the selection and enrichment of Fusarium populations with increased aggressiveness. [ABSTRACT FROM AUTHOR]

This study examines the CO2-mediated influence of plant resistance on crown rot dynamics under continuous cropping of partially resistant wheat line 249 and the susceptible cultivar Tamaroi. Disease incidence, severity, deoxynivalenol and Fusarium biomass were assessed after each cycle in microcosms established at ambient and 700 mg kg-1 CO2 using soil and stubble of these wheat lines from a field experiment with free to air CO2 enrichment. Monoconidial isolates from wheat stubble were collected initially, and after five cropping cycles, to compare the frequency and aggressiveness of Fusarium species in the two populations. Aggressiveness was measured using a high-throughput seedling bioassay. At elevated CO2, the higher initial incidence in Tamaroi increased with cropping cycles, but incidence in 249 remained unchanged. Incidence at ambient CO2 did not change for either line. Elevated CO2 induced partial resistance in Tamaroi, but not in 249. Increased Fusarium biomass in wheat tissue at elevated CO2 matched raised deoxynivalenol of the stem base in both lines. After five cycles of continuous wheat cropping, aggressiveness increased in pathogenic F. culmorum and F. pseudograminearum by 110%, but decreased in weakly pathogenic F. equiseti and F. oxysporum by 50%. CO2 and host resistance interactively influenced species frequency, and the highly aggressive F. pseudograminearum became dominant on Tamaroi irrespective of CO2 concentration, while its frequency declined on 249. This study shows that induced resistance at elevated CO2 will not reduce crown rot severity, or impede the selection and enrichment of Fusarium populations with increased aggressiveness. [ABSTRACT FROM AUTHOR]

Fusarium pseudograminearum (Fp), the causative fungal pathogen of the diseases Fusarium crown rot, is an important constraint to cereals production in many countries including Australia. Fp produces a number of secondary metabolites throughout its life cycle. One of these metabolites, the cyclic lipopeptide fusaristatin A, is encoded by a specific gene cluster containing a polyketide synthase and a three-module non-ribosomal peptide synthetase. However, a recent survey of Fp populations across Australia suggests that this cluster may only be present in a subset of isolates from Western Australia (WA). In this study, we screened 319 Fp isolates from WA and 110 Fp isolates from the Australian eastern states of New South Wales, Victoria, Queensland and South Australia to examine the distribution of this gene cluster among Australian Fp populations. The fusaristatin A gene cluster was found to be present in ~50% of Fp isolates from WA but completely absent in Fp isolates from eastern states. To determine its potential function, mutants of the fusaristatin A gene cluster were generated by disrupting the non-ribosomal peptide synthetase and polyketide synthase genes simultaneously in two different parental backgrounds. The mutants showed increased growth rates and were significantly more aggressive than their respective parental strains on wheat in crown rot pathogenicity assays. This suggested that fusaristatin A has a negative effect on fungal development and aggressiveness. The possible reasons for the geographically restricted presence of the fusaristatin A gene cluster and its role in fungal biology are discussed., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2019. Published by Elsevier Inc. All rights reserved.)

Surveys for crown rot (FCR) and head blight (FHB) of Algerian wheat conducted during 2014 and 2015 revealed that Fusarium culmorum strains producing 3-acetyl-deoxynivalenol (3ADON) or nivalenol (NIV) were the causal agents of these important diseases. Morphological identification of the isolates (n FCR=110, n FHB=30) was confirmed by sequencing a portion of TEF1. To assess mating type idiomorph, trichothecene chemotype potential and global population structure, the Algerian strains were compared with preliminary sample of F. culmorum from Italy (n=27), Australia (n=30) and the United States (n=28). A PCR assay for MAT idiomorph revealed that MAT1-1 and MAT1-2 strains were segregating in nearly equal proportions, except within Algeria where two-thirds of the strains were MAT1-2. An allele-specific PCR assay indicated that the 3ADON trichothecene genotype was predominant globally (83.8% 3ADON) and in each of the four countries sampled. In vitro toxin analyses confirmed trichothecene genotype PCR data and demonstrated that most of the strains tested (77%) produced culmorin. Global population genetic structure of 191 strains was assessed using nine microsatellite markers (SSRs). AMOVA of the clone corrected data indicated that 89% of the variation was within populations. Bayesian analysis of the SSR data identified two globally distributed, sympatric populations within which both trichothecene chemotypes and mating types were represented., (Copyright © 2017. Published by Elsevier Inc.)

Fusarium graminearum and 21 related species comprising the F. sambucinum species complex lineage 1 (FSAMSC-1) are the most important Fusarium Head Blight pathogens of cereal crops world-wide. FSAMSC-1 species typically produce type B trichothecenes. However, some F. graminearum strains were recently found to produce a novel type A trichothecene (NX-2) resulting from functional variation in the trichothecene biosynthetic enzyme Tri1. We used a PCR-RFLP assay targeting the TRI1 gene to identify the NX-2 allele among a global collection of 2515 F. graminearum. NX-2 isolates were only found in southern Canada and the northern U.S., where they were observed at low frequency (1.8%), but over a broader geographic range and set of cereal hosts than previously recognized. Phylogenetic analyses of TRI1 and adjacent genes produced gene trees that were incongruent with the history of species divergence within FSAMSC-1, indicating trans-species evolution of ancestral polymorphism. In addition, placement of NX-2 strains in the TRI1 gene tree was influenced by the accumulation of nonsynonymous substitutions associated with the evolution of the NX-2 chemotype, and a significant (P<0.001) change in selection pressure was observed along the NX-2 branch (ω=1.16) in comparison to other branches (ω=0.17) in the TRI1 phylogeny. Parameter estimates were consistent with positive selection for specific amino-acid changes during the evolution of NX-2, but direct tests of positive selection were not significant. Phylogenetic analyses of fourfold degenerate sites and intron sequences in TRI1 indicated the NX-2 chemotype had a single evolutionary origin and evolved recently from a type B ancestor. Our results indicate the NX-2 chemotype may be indigenous, and possibly endemic, to southern Canada and the northern U.S. In addition, we demonstrate that the evolution of TRI1 within FSAMSC-1 has been complex, with evidence of trans-species evolution and chemotype-specific shifts in selective constraint., (Published by Elsevier Inc.)

Warmer temperatures associated with climate change are expected to have a direct impact on plant pathogens, challenging crops and altering plant disease profiles in the future. In this study, we have investigated the effect of increasing temperature on the pathogenic fitness of Fusarium pseudograminearum, an important necrotrophic plant pathogen associated with crown rot disease of wheat in Australia. Eleven wheat lines with different levels of crown rot resistance were artificially inoculated with F. pseudograminearum and maintained at four diurnal temperatures 15/15°C, 20/15°C, 25/15°C and 28/15°C in a controlled glasshouse. To quantify the success of F. pseudograminearum three fitness measures, these being disease severity, pathogen biomass in stem base and flag leaf node, and deoxynivalenol (DON) in stem base and flag leaf node of mature plants were used. F. pseudograminearum showed superior overall fitness at 15/15°C, and this was reduced with increasing temperature. Pathogen fitness was significantly influenced by the level of crown rot resistance of wheat lines, but the influence of line declined with increasing temperature. Lines that exhibited superior crown rot resistance in the field were generally associated with reduced overall pathogen fitness. However, the relative performance of the wheat lines was dependent on the measure of pathogen fitness, and lines that were associated with one reduced measure of pathogen fitness did not always reduce another. There was a strong correlation between DON in stem base tissue and disease severity, but length of browning was not a good predictor of Fusarium biomass in the stem base. We report that a combination of host resistance and rising temperature will reduce pathogen fitness under increasing temperature, but further studies combining the effect of rising CO2 are essential for more realistic assessments., (© 2015 John Wiley & Sons Ltd.)

Crown rot and head blight of wheat are caused by the same Fusarium species. To better understand their biology, this study has compared 30 isolates of the three dominant species using 13 pathogenic and saprophytic fitness measures including aggressiveness for the two diseases, saprophytic growth and fecundity and deoxynivalenol (DON) production from saprophytic colonization of grain and straw. Pathogenic fitness was generally linked to DON production in infected tissue. The superior crown rot fitness of Fusarium pseudograminearum was linked to high DON production in the stem base tissue, while Fusarium culmorum and Fusarium graminearum had superior head blight fitness with high DON production in grains. Within each species, some isolates had similar aggressiveness for both diseases but differed in DON production in infected tissue to indicate that more than one mechanism controlled aggressiveness. All three species produced more DON when infecting living host tissue compared with saprophytic colonization of grain or straw, but there were significant links between these saprophytic fitness components and aggressiveness. As necrotrophic pathogens spend a part of their life cycle on dead organic matter, saprophytic fitness is an important component of their overall fitness. Any management strategy must target weaknesses in both pathogenic fitness and saprophytic fitness., (© 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.)

An isolated occurrence of Fusarium head blight (FHB) of wheat was detected in the south-west region of Western Australia during the 2003 harvest season. The molecular identity of 23 isolates of Fusarium spp. collected from this region during the FHB outbreak confirmed the associated pathogens to be F. graminearum, F. acuminatum or F. tricinctum. Moreover, the toxicity of their crude extracts from Czapek-Dox liquid broth and millet seed cultures to brine shrimp (Artemia franciscana) was associated with high mortality levels. The main mycotoxins detected were type B trichothecenes (deoxynivalenol and 3-acetyldeoxynivalenol), enniatins, chlamydosporol and zearalenone. This study is the first report on the mycotoxin profiles of Fusarium spp. associated with FHB of wheat in Western Australia. This study highlights the need for monitoring not just for the presence of the specific Fusarium spp. present in any affected grain but also for their potential mycotoxin and other toxic secondary metabolites.

Sheep grazing in Western Australia can partially or completely refuse to consume annual Medicago pods contaminated with a number of different Fusarium species. Many Fusarium species are known to produce trichothecenes as part of their array of toxigenic secondary metabolites, which are known to cause feed refusal in animals. This study reports the identity of Fusarium species using species-specific PCR primers and a characterization of the toxigenic secondary metabolites produced by 24 Fusarium isolates associated with annual legume-based pastures and particularly those associated with sheep feed refusal disorders in Western Australia. Purification of the fungal extracts was facilitated by a bioassay-guided fractionation using brine shrimp. A number of trichothecenes (3-acetyldeoxynivalenol, deoxynivalenol, fusarenon-X, monoacetoxyscirpenols, diacetoxyscirpenol, scirpentriol, HT-2 toxin and T-2 toxin), enniatins (A, A1, B, and B1), chlamydosporol and zearalenone were identified using GC/MS and/or NMR spectroscopy. Some of the crude extracts and fractions showed significant activity against brine shrimp at concentrations as low as 5 μg ml(-1), and are likely to be involved in the sheep feed refusal disorders. This is the first report of chlamydosporol production by confirmed Fusarium spp.; of the incidence of F. brachygibbosum and F. venenatum in Australia and of F. tricinctum in Western Australia; and of mycotoxin production by Fusarium species from Western Australia.

This article reports a lack of pathogenic specialization among Australian Fusarium graminearum and F. pseudograminearum causing crown rot (CR) of wheat using analysis of variance (ANOVA), principal component and biplot analysis, Kendall's coefficient of concordance (W), and κ statistics. Overall, F. pseudograminearum was more aggressive than F. graminearum, supporting earlier delineation of the crown-infecting group as a new species. Although significant wheat line-pathogen isolate interaction in ANOVA suggested putative specialization when seedlings of 60 wheat lines were inoculated with 4 pathogen isolates or 26 wheat lines were inoculated with 10 isolates, significant W and κ showed agreement in rank order of wheat lines, indicating a lack of specialization. The first principal component representing nondifferential aggressiveness explained a large part (up to 65%) of the variation in CR severity. The differential components were small and more pronounced in seedlings than in adult plants. By maximizing variance on the first two principal components, biplots were useful for highlighting the association between isolates and wheat lines. A key finding of this work is that a range of analytical tools are needed to explore pathogenic specialization, and a statistically significant interaction in an ANOVA cannot be taken as conclusive evidence of specialization. With no highly resistant wheat cultivars, Fusarium isolates mostly differ in aggressiveness; however, specialization may appear as more resistant cultivars become widespread.

Fusarium culmorum is a major pathogen of wheat and barley causing head blight and crown rot in cooler temperate climates of Australia, Europe, West Asia and North Africa. To better understand its evolutionary history we partially sequenced single copy nuclear genes encoding translation elongation factor 1-α (TEF), reductase (RED) and phosphate permease (PHO) in 100 F. culmorum isolates with 11 isolates of Fusarium crookwellense, Fusarium graminearum and Fusarium pseudograminearum. Phylogenetic analysis of multilocus sequence (MLS) data using Bayesian inference and maximum parsimony analysis showed that F. culmorum from wheat is a single phylogenetic species with no significant linkage disequilibrium and little or no lineage development along geographic origin. Both MLS and TEF and RED gene sequence analysis separated the four Fusarium species used and delineated three to four groups within the F. culmorum clade. But the PHO gene could not completely resolve isolates into their respective species. Fixation index and gene flow suggest significant genetic exchange between the isolates from distant geographic regions. A lack of strong lineage structure despite the geographic separation of the three collections indicates a frequently recombining species and/or widespread distribution of genotypes due to international trade, tourism and long-range dispersal of macroconidia. Moreover, the two mating type genes were present in equal proportion among the F. culmorum collection used in this study, leaving open the possibility of sexual reproduction., (Copyright © 2010 The British Mycological Society. Published by Elsevier Ltd. All rights reserved.)